This invention is directed to the construction of a hydraulic turbo-machine such as a pump or pump turbine, and in particular to a wicket gate stem seal to preclude ingress of contaminated water into the bearings of the wicket gates.
In the case of turbo-machines such as Francis turbines or pump turbines having adjustable wicket gates the problem arises under conditions of operation with contaminated water containing abrasive particles that the bushings of the wicket gates may become infiltrated by the contaminated water, particularly under conditions of shut-down when the wicket gates are in the fully closed condition, or under base load conditions, when the setting of the wicket gates can remain unchanged for a matter of weeks at a time. The presence of such contaminants can result in a tendency of the wicket gate spindles to seize in their bushings under such conditions of operation, or to generate wear in the spindles and bushings and so cause inaccuracy in gate settings which can lead to overload of the control mechanism. Ultimately these effects of contamination can lead to machine failure, or at least necessitate taking the machine out of service, for purposes of maintenance. In as much as the wicket gates are normally relied upon to regulate machine operation, including the shutting down of the machine, the malfunctioning of the wicket gates can lead to very serious consequences.
In the case of gas turbines, these machines are not considered to be analogous in their structure to water pumps and turbines, on account of the extreme differences in ambient temperature conditions, dynamic forces acting on the respective guide vanes, and totally different functional requirements between a hot and compressible gaseous working fluid and a cold, incompressible liquid working fluid. In gas turbine technology it is well known to introduce air as a lubricating fluid to the bearings of the variable guide vanes, as shown in U.S. Pat. No. 3,542,484, Mason, issued Nov. 24, 1970. Mason also shows a loading spring to axially load his guide vanes radially outwardly against the bearing seating, under shut-down conditions. The use of air as a cooling medium for the bearings of gas turbine guide vanes is shown in U.S. Pat. No. 3,582,231 Zerlauth, issued June 1, 1971.
Sealing of the end surfaces of wicket gates is shown in U.S. Pat. No. 3,947,147, Loktaeva et al, issued Mar. 30, 1976, in which an annular gasket is located between an axial end surface of the wicket gate and the rim of the housing.
The prior art does not show the use of either gaseous or liquid fluid for purging purposes to avoid contamination of the vane bearings.
Furthermore, the use of an axially spring loaded seal also is not known. In the case of U.S. Pat. No. 3,685,921, Dekeyser, issued Aug. 22, 1972, the blades of a gas turbine guide ring are biased radially inwardly against an inner casing.
The problem of coping with contaminated water for driving a turbine, bearing abrasive solid particles is in no way approached in the prior art. In the extreme, abrasive particulate content as high as about 40% by weight has been known, on an irregular basis, and the present disclosure represents one effort to minimize some of the effects that such conditions may produce.